Our hempcrete house near Dunbar is going up much faster than we expected. In fact, the construction process is quicker than for an equivalent timber-framed house.
This is because the qualities of all the components of a traditional wall are met by the hempcrete alone – with the exception of the structural frame. Unfortunately Hempcrete’s structural strength is not recognised by UK building standards, which means that an over-specified timber frame had to be built before the hempcrete was sprayed around it. All that is left to do on the Dunbar house is to lime-render the outside and plaster the inside.
The hempcrete performs the job of insulation, breathable membrane and provides thermal mass. This means it manages moisture movement and moderate temperatures. Therefore the house will require less energy to heat and cool than most conventional homes. It is made 100% of natural materials. There will be no toxic emissions. This, along with the moisture control makes a hempcrete house an extremely healthy one. The softwood timber frame does not even need treatment against rot because the hempcrete draws the moisture out of the timber.
Hempcrete also has extremely good environmental credentials – this house will sequester more carbon than it emits. This is explained in detail by Graham Durant, founder of Nofolk-based Hemp-Lime Spray Limited’s, in a recent blog about hemp’s sustainability credentials as a building material.
The hempcrete was hand-cast for the lowest one metre, where access was problematic, and sprayed above that height – a very efficient means of applying the material. These walls took 24 days to complete but would have been twice as quick with an experienced workforce. On our job, Graham was training two apprentices. Graham is a joy to work with as someone who completely understands the material and takes great pride in their work.
I was surprised that work was able to continue during the recent severe winds and heavy rain including storm Babet. The team continued throughout, working internally or on the leeward side of the house.
The hemp shiv (chopped up, woody core of the hemp plant) used on the Dunbar site was grown in France. Although hemp can be sourced from England, the quality is not suitable for a spray gun. Once the appropriate type of hemp is grown in the UK, and the market expands, hempcrete should become even better value for money.
And lastly, the house feels good. The solidity and thickness of the walls give it a massive sculptural quality quite different to a timber frame building. The plasticity of the material make it is easy to personalise details with rounded corners and other features.